Resin compositions made by blending polyolefins and EVOH are well known (see Patent Document 1). However, these resin compositions are generally poor in compatibility with each other and, hence, when formed into film, sheet, bottle or the like by extrusion molding, the compositions tend to generate nonuniform phase-separated foreign matters. The number of the foreign matters increases particularly during long periods of operation and the appearance of the molded articles is significantly impaired (reduction of long-run processability). Additional problems, such as formation of lip stain around the die exit at the time of the extrusion process of the resin compositions, are also known. This lip stain can become mixed in the molded articles, lowering their quality.
It is known that blending higher fatty acid metal salts having 8 to 22 carbon atoms, ethylenediaminetetraacetate metal salts, and/or such as hydrotalcite compounds is effective in improving the insufficient compatibility between polyolefin and EVOH (see Patent Documents 1 and 2). In addition to the combination, it is disclosed that, in addition to blending hydrotalcite based compounds and higher fatty acid metal salts having 8 carbon atoms or more in the mixture of a polyolefin and an EVOH, the addition of boron compounds, phosphoric acids and/or alkali (alkali-earth) hydrogen phosphates, or lower fatty acid metal salts having 7 carbon atoms or less, or the like, improves long-run processability and heat resistance of compositions mainly comprising a polyolefin and an EVOH at the time of melt molding (physical property retention at repeated heating accompanying recycling) (see Patent Documents 3, 4 and 5). In these documents, however, the evaluation of fish-eye formation at the time of film molding is done by observing the number of fish-eye particles having a diameter of 0.2 mm or more formed per 100 cm2.
It is also disclosed that saponified ethylene-vinyl acetate copolymers having an ethylene content of 68 to 98 mol % and having a degree of saponification of vinyl acetate units of 20% or more (may be abbreviated as S-EVOH hereinafter) may be blended as resin compositions capable of preventing wavy pattern formation on the molded articles surface in addition to using at least one component selected from higher fatty acid metal salts having 8 to 22 carbon atoms, ethylenediaminetetraacetate metal salts, and hydrotalcites described above to a polyolefin and an EVOH, at the time of melt-molding resin compositions comprising a polyolefin and an EVOH. The wavy patterns arise from flow anomalies due to insufficient compatibility at the time of melt molding. In this manner, the compatibility of the obtained resin compositions is improved and the wavy patterns on the molded article surface are prevented, and thus the effective reuse of scrap compositions such as regrinds is disclosed (see Patent Document 6).
It has also been disclosed that by adding an acid graft-modified polyolefin based resin and a polyalcohol compound to recycled materials of layered products including thermoplastic resin layers and EVOH layers, the resin compositions showing no gelation at the time of melt molding, producing no wavy patterns or fish-eyes on the molded articles, having an excellent long-run processability, and capable of preventing the phase-separated foreign matter (lip stain), can be obtained (see Patent Document 7). However, in this document, evaluation of fish-eye formation is done by observing the number of fish-eye particles having a diameter of 0.4 mm or more formed per 100 cm2 in the regrind layer of the layered products.
In addition, a method for manufacturing vinyl acetate based polymers by the addition of a conjugated polyene compound having a boiling point of 20° C. or more to an ethylene-vinyl acetate copolymer, and a method for manufacturing saponified vinyl acetate based polymers by the saponification of the vinyl acetate based polymers obtained in this method, have also been disclosed. EVOH obtained by these methods is considered of high quality showing minimal coloration and minimal formation of gel-like hard spots at the time of molding (see Patent Document 8).
Also, resin compositions made by blending EVOH with an ethylene-vinyl acetate copolymer having an ethylene content of 60 to 98 mol % and S-EVOH, and multilayer structures consisting of at least 2 layers including the resin composition layers, have been disclosed. According to this reference, resin compositions having excellent gas barrier properties and improved flexibility and transparency can be obtained (see Patent Document 9).
According to the arts disclosed in Patent Documents 2 to 7, compatibility between EVOH and polyolefin in the resin compositions made by blending polyolefin and EVOH can be greatly improved, resulting in improved appearance of the molded articles. However, in the current environment-responsive trend (volume reduction of packaging materials and waste materials), demand for thinning of cups, bottles and films is on the increase. Therefore, the need for reducing the poor appearance due to insufficient dispersion at a more micro-scale level and flow anomalies of resin compositions made by blending polyolefin and EVOH is also increasing. For traditional packaging materials, which were relatively thick, there were no such problems because of the low transparency and the like. In Patent Document 8, the art of reducing the gel-like hard spots in molded articles made of EVOH alone is disclosed. In Patent Document 9, the art of improving the flexibility of molded articles made mainly of EVOH alone is disclosed. No mention or hint of resin compositions made by blending EVOH and polyolefin is found in Patent Documents 8 and 9.